Pumps

Image Gallery

Research

Engine Driven Pumps

If you are preparing an old boat for blue water sailing, the inadequacy of even a large electric bilge pump might lead you to consider an engine driven pump to deal with major water intrusion. Such a pump will operate for as long as you can keep the engine running, and the capacity of the large engine-driven pumps put electric bilge pumps into the “wimpy” class. A commonly seen model from Jabsco is rated at 4,980 gph and will deliver close to even that with 6 feet of lift. [an engine pump will deliver a lot more]. (This Old Boat, p. 349)

…make certain that the pump you select is self priming. (This Old Boat, p. 349)

I think a manual clutch is a better choice than an electric one because it keeps the pump independent of the electrical system. Unless your main engine is rigidly mounted (no flexible mounts), you will need to mount the pump to the engine rather than the boat. Otherwise the independent oscillations will subject the bearings in both pump and engine to destructive shock loading.

Pumps are standard, but the mounting bracket will be custom-made. Use heavy-gauge steel for the bracket. The mount must be adjustable or incorporate an idler pulley to allow tensioning the appropriate belt. Size the pulleys correctly to get maximum output from the pump. (This Old Boat, p. 349)

Engine-driven pumps are usually flexible-impeller types and don’t handle solids well, so the pickup hose should lead into a strum box – a strainer….(This Old Boat, p. 349)

Make a habit of rotating the pump by hand everytime you check the oil to keep the impeller from taking a set. Run or pour a few gallons of fresh water into the bilge and engage the pump occasionally to exercise it, but do not allow it to run dry. Check the belt tension after you run the pump. Open the pump and inpsect the impeller once a year. Replace it if it shows any cracks or signs of hardening. Lubricating the chamber with a little petroleum jelly will reduce the wear and stress on the impeller when the pump is priming. (This Old Boat, p. 349)

Electric Pumps

Leave some extra wiring connected to pumps, so it’s easier to move around. (All in the Same Boat, p. 80)

As designated machinist mate, I have spent a lot of time upside down in the bilge trying to find and fix a balky pump. I decided that all of my pumps would be in one place and easy to get to. I installed a pump board just forward of the companion way. (source offline)

Make sure very pump aboard is in an accessible location. If one stops your life could depend on how fast you can make repairs and resume operation. Leave enough space around the pump to fit both your hands and necessary tools. (Upgrading the Cruising Sailboat, p. 108)

A bilge pump has two separate functions: to remove small amounts of water from the boat – such as from a dripping shaft seal – on a routine basis; and to help remove large amounts of water in a catastrophic event. (Cruising Handbook, p. 217)

…installed bilge pumps almost never produce their rated flow; in fact, the majority don’t even come close….typical installations using a relatively large (3,000 gallons per hour ) submersible pump as an example. It turns out that this pump almost never produces even half its rated output, and at times (especially if the boat’s batteries are a little low and the boat is heeled), pumps as little as 700 gph, which is under 25% of rated output. There are other pump types that do not show this dramatic loss of performance, specifically electric diaphragm pumps….despite their limitations, in my opinion centrifugal pumps are the best of the bunch. (Cruising Handbook, p. 220)

To quote the report [from the University of Rhode Island], “prolonged stagnation of bilge water is the surest method for destroying hull integrity.” (This Old Boat, p. 347)

What does the capacity of the pump have to do with how much water stands in the bilge?…The link is not the size of the pump; it’s the size of the hose. On my old boat the most direct route from the pump to overboard discharge requires about 9 feet of hose – probably shorter than the norm. The high-capacity pump necessitates a 1 1/2″ hose. When the pump shuts off, that hose is full – like a 9′ tall stein. All that water flows back through a centrifugal pump and back into the bilge. A check valve might initially keep the water from draining back, but deposits of debris from the bilge water would soon prevent the valve from sealing. Besides, a check valve in a bilge pump discharge line is a bad idea because it reduces the output and introduces a real risk of blockage. The only safe way to minimize the amount of water draining back into the bilge is to keep the run as short as possible and to use the smallest hose you can. Discharging the water through a 1/2″ hose rather than a 1/ 1/2″ hose reduces the amount of water that drains back by 89%! Unfortunately it also imposes a similar reduction on the amount of water you can pump out. Reduce the 1 1/2″ discharge hose on a 3,700 gph pump to 1/2″ and you cut the output to less than 400 gph. This is woefully inadequate for any serious breach. (This Old Boat, p. 347)

…purchase a small (500 gph or less) pump with an internal float switch. Such a pump should cost less than a reliable float switch for the high-capacity pump – a switch you are going to omit. In the event of a major water intrusion, you will manually switch on the high-capacity pump with a clearly labeled toggle switch near the companionway. The money you don’t spend on the float switch will pay for the small automatic pump….Install the 400 gph pump in the lowest part of the bilge and wire it through a fuse directly to one of the batteries. A pump this size will have a 3/4″ outlet, but insert a reducer in the line and run 1/2″ hose as directly as possible to a discharge fitting installed in the hull just below the rail…mount the high capacity pump to the plywood bridge…Connect the pump outlet to a second discharge fitting with 1 1/2″ hose. The size of the hose is no longer a concern. If the pump is operated, any water that drains back into the bilge will be removed by the smaller pump. This dual pump installation will result in a bilge that is bone dry if you maintain the stuffing box. The small pump, because of it’s size, pumps the water level lower to begin with, and the small discharge hose minimizes the amount of water that drains back. The shallow puddle that does remain soon evaporates absorbed by the air instead of the hull. An added advantage of this arrangement is that the expensive high-capacity pump, because it sits high and dry, should never require replacement. (This Old Boat, p. 348)

Leaks often start small, growing more serious over time but if your pump is keeping your bilge dry, you don’t know you have a problem until it is a big problem. The solution to this is an electronic counter that keeps track of the number of pump cycles. (This Old Boat, p. 349)

If you have a more restricted budget, you can adapt a $5 pedometer with a $5 reed relay (RadioShack part number 275-233or any other 12V relay). Electrical contact by a spring loaded pendulum in the pedometer normally advances the counter. If you open the pedometer case, you should be able to remove the pendulum and delicately solder the switch wires for the relay to the two contact surfaces. Now a 12V current across this relay closes the reed switch and advances the counter. (This Old Boat, p. 349)

Float Switches

Water Witch – haven’t heard good things, easy to foul the sensors and they lose their ability to function (www.waterwitchinc.com/)

Float switches that turn on and off at the same height are constantly turning the pump on and off each time the water laps the sensing device. (Upgrading the Cruising Sailboat, p. 108)

A mechanism is required to turn a pump on and off. There is much to be said for making it a manual switch because it forces one to regularly check the state of the bilge, however, in practice, the boating public demands an automatic switch that is generally backed up with a manual override. (Cruising Handbook, p. 222)

The most common switch is a float switch, but there are also switches operated by air pressure and at least three forms of electronic switch. The variety of switches is testimony to the fact that no one type is universally satisfactory in bilge-pumping applications. The popular float switches are prone to…trash jamming the hinge so that the switch is either locked “on” or “off”…Most switches have optional covers that filter out the worst debris: this type should always be installed. Beyond this, there are various electrical modes of failure. Many of the switches are built with lightweight electrical components that have a bad habit of burning out. Any switch needs to have a continuous current rating (amperage) at least equal to the amps rating of the pump to which it is attached, and preferably a substantially higher rating. (Cruising Handbook, p. 222)

The location of a switch relative to its pump is important. If a switch is mounted in a position where it is laterally offset from the pump intake, when the boat is heeled on one tack the switch will not respond until considerably more water is in the bilge than is needed for a level-state response. On the other tack, there is a very real danger that the switch will stay energized after the pump has sucked itself dry, causing the pump to run continuously…To minimize these problems, a float switch should always be mounted as close to its pump as possible and in the same fore-and-aft plane…many switches are simply clipped into the base of the pump;, in this case, it is essential o ensure that the switch is aligned fore and aft; if it is set to one side, the pump will definitely run dry on one tack or the other. (Cruising Handbook, p. 222)

Even if a switch is mounted in the same fore-and-aft plane as its pump, when the boat is pounding into a head sea or rolling from side to side, the action of a small amount of water surging backward and forward in the bilge can flick the switch on and off until eventually something fails. This situation also creates an unnecessary drain on the batteries. A similar but even more annoying condition occurs when the bilge pump and switch are installed in a deep, narrow sump, with a moderately long discharge hose from the pump to the overboard through-hull. Every time the pump is shut down, the water in the hose flows back down into the bilge, raising the water level of the bilge water – sometimes to the point at which the pump kicks back on. The pump keeps on cycling until the battery is dead. I know of no practical way to deal with this, other than using a different type of switch (the Ultimate switches come with a series of operating differentials from as little as ¾” up to 2 ½”; greater differentials, up to 1 – 2’, are available as special-order items). (Cruising Handbook, p. 223)

Pivoting arm switches, the least expensive and most common design, are a study in simplicity but generally less reliable than they should be given their responsibility. A housing over the float can avoid one vulnerability, jamming by solid debris, but the pivot in nearly all pivoting-arm switches eventually stick (This Old Boat, p. 348)

The floating doughnut style of switch with a free float around a central rod inside a perforated tube is mechanically more reliable but also more expensive. (This Old Boat, p. 348)

Greywater Pumps

Amel has a BIG manual electric bilge pump but the previous owner put in a BIG Rule 4000 gph and a float switch way down in the bottom. The Rule doesn’t do well with food solids that make it into the bilge, but I just pull the power to it and flush out the solids with soapy water and the big Amel OEM bilge pump ever so often, when I think of it. (http://www.waterwitchinc.com/)

Diaphram pumps were suggested that they wouldn’t “clog with hair”

There was some discussion on the “Water Witch Bilgeswitch” and other sensor type sensors which automatically sense water, but the general sense of these was that their sensors clog up fairly easily, this would especially be the case when used in a greywater tank. (http://www.waterwitchinc.com/)

Inlet & Outlet

There is no best place to discharge a bilge pump. Locations that may be above water at dock may disappear below the surface when heeled over under way. And, as bilge water is often oily, its the last thing you want in the cockpit or on deck, when sure footing is of great importance. I favor a thru-hull just under the stern or in the side of the hull several feet above the waterline. (Upgrading the Cruising Sailboat, p. 98 – 9)

As water passes through a hose or pipe, the interior surface causes friction and retards the flow. To minimize friction, choose hose with a smooth interior wall; keep the length as short as possible. Avoid sharp bends. Also, the higher the distance the water has to be lifted, the less efficient the pump. Hose routed to thru -hulls above the waterline that are not fitted with sea cocks should be routed as high as possible to prevent water from running back into the boat in the event the thru-hull becomes submerged. Some advocate looping the hose to prevent siphoning water back into the boat. But this creates unnecessary friction. A better solution is to install a sea cock or at least an in-line valve that can be opened and closed. (Upgrading the Cruising Sailboat, p. 99)

Sometimes the diameter of the discharge hose will be larger than the intake, in fact, a pump with a discharge opening 25% larger than its intake will be more efficient. (Upgrading the Cruising Sailboat, p. 108)

Try not to locate the discharge where you come aboard from the dinghy. Several inches higher and not directly above the small pump (This Old Boat, p. 348)

It is imperative to have this discharge clear of the water on all points of sail or the ocean will siphon in when the pump shuts off. (This Old Boat, p. 348)

The pump’s intake should be in a sump in the deepest part of the bilge and should have a screen to avoid clogging. (Desirable and Undesirable Characteristics of Offshore Yachts, p. 125)

Protect the pickup with a bilge strainer….you can fabricate from scrap PVC. You will need a strainer that will not restrict the pump’s capacity and will be difficult to clog. You can fabricate an excellent strainer from a foot of 3″ PVC pipe Cap one end and fit the other end with a threaded adapter and a hose connector to match your pump….drill the bejesus out of the pipe with a sharp 3/8″ bit….more holes than plastic. (This Old Boat, p. 349)

The discharge hose must maintain a steady rise at all angles of heel up to its through-hull or vented loop. (Cruising Handbook, p. 220)

Manual Pumps

The bilge pump usually involves the cockpit. I believe that the very best bilge pump is a diaphragm pump located just under the cabin sole; when it really becomes necessary to remove a lot of water, there is nothing like it. Still, bilge pumpers below sometimes suffer from seasickness, so it’s a good idea to have a manual bilge pump that can be operated from the cockpit. The socket for the pump handle should be located so that it can be inserted and worked without the necessity of opening a sea locker in rainy or rough weather – say, into the side of the cockpit well or on a cockpit seat. (Desirable and Undesirable Characteristics of Offshore Yachts, p. 125)

Locating the pump is…a critical decision. A shorthanded crew at sea will want one pump easily operated by the helmsman. This means locating the pump either under the cockpit floor or under or beside cockpit seats. before cutting any holes, pretend you’re sitting at the wheel or tiller, braced for green seas. See where the lever handle would be most convenient. Take into account the amount of throw in the lever also, as you won’t want to have to move too far from the helm. Another pump, mounted in the bilge and operated by a person sitting on a bunk or on the cabin sole, is good insurance. (Upgrading the Cruising Sailboat, p. 99)

To deal with water that gets below, all cockpits need a bilge pump that can be operated from the helm station without having to open any lockers. The pump needs to be plumbed to the lowest point in the bilge. Large capacity diaphragm pumps are by far, the best in this application. Seats should be designed to drain at up to a 30-degree angle of heel. (Cruising Handbook, p. 93)

Don’t put all your faith in a manual pump. The biggest ones around (Edson) are rated at 30 gallons per minute….it is your last line of defense, and you should install the largest and least tiring pump you can find. (This Old Boat, p. 349)

A foot pump installation also requires a spout mounted over the sink. The spout mounts through a hole in the counter and is held in place by a nut on the underside. The supply hose is clamped to the inlet side of the foot pup. A second length of hose connects to the outlet side of the pump the hose fitting at the bottom of the spout. (This Old Boat, p. 320)

Type – Centrifugal

A centrifugal pump is a rotodynamic pump that uses a rotating impeller to increase the pressure of a fluid. Centrifugal pumps are commonly used to move liquids through a piping system. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute chamber (casing), from where it exits into the downstream piping system. Centrifugal pumps are used for large discharge through smaller heads. (http://en.wikipedia.org/wiki/Centrifugal_pump)

Cons – Cavitation—the NPSH of the system is too low for the selected pump. Wear of the Impeller—can be worsened by suspended solids, Corrosion inside the pump caused by the fluid properties, Overheating due to low flow, Leakage along rotating shaft, Lack of prime—centrifugal pumps must be filled (with the fluid to be pumped) in order to operate, Surge (http://en.wikipedia.org/wiki/Centrifugal_pump)

The primary reason why they perform so poorly is that the pumps are rated in a totally unrealistic environment that includes no discharge piping and no back pressure on the system. As soon as the resistance created by a discharge hose – and the resistance caused by the need to actually lift the water up and out of a boat – are factored in, the pump’s output dives. This cumulative resistance is known as head pressure. (Cruising Handbook, p. 220)

The single greatest improvement in the performance of a centrifugal pump comes from reducing the head pressure. Given that the vertical lift component is more or less fixed by physical dimensions of a boat, the only component of head pressure that can be readily reduced is that which is created by the piping run. There is a clear need to use a hose no smaller than the pump’s outlet, to keep the hose run as short and direct as possible, and to avoid any additional resistance such as that imposed by check valves or dirty suction filters. (Cruising Handbook, p. 220)

…centrifugal bilge pumps are typically rated at their theoretical maximum deliver with zero lift and equally inexplicably at 13.6 volts ( for 12-volt pumps). If this is not dishonest, it is certainly misleading. If you could configure your bilge pump for zero lift, a drain plug should serve. With the discharge fitting 5 – 6 feet above the bilge (the minimum lift in even a modest sailboat), a centrifugal pump is unlikely to expel water from your boat at more than 1/2 the rated capacity. Output can decline by half again when you factor in real-world battery voltage. (This Old Boat, p. 347)

Type – Diaphragm

Positive displacement pump that uses a combination of the reciprocating action of a rubber, thermoplastic or teflon diaphragm and suitable non-return check valves to pump a fluid...When the volume of a chamber of either type of pump is increased (the diaphragm moving up), the pressure decreases, and fluid is drawn into the chamber. When the chamber pressure later increases from decreased volume (the diaphragm moving down), the fluid previously drawn in is forced out. Finally, the diaphragm moving up once again draws fluid into the chamber, completing the cycle. This action is similar to that of the cylinder in an internal combustion engine…. (http://en.wikipedia.org/wiki/Diaphragm_pump)

Con – can cause water hammer (or, more generally, fluid hammer) which is a pressure surge or wave resulting when a fluid (usually a liquid but sometimes also a gas) in motion is forced to stop or change direction suddenly (momentum change). Water hammer commonly occurs when a valve is closed suddenly at an end of a pipeline system, and a pressure wave propagates in the pipe. It may also be known as hydraulic shock. (http://en.wikipedia.org/wiki/Diaphragm_pump)

A good diaphragm pump will not easily clog and will be able to pass small bits of wood or other debris. Most diaphragm pumps jam when foreign objects stick in the valve, keeping it open and preventing a watertight seal in the chamber. Jamming isn’t supposed to occur in the diaphragm chamber unless a long narrow object (e.g. a stick) manages to pass through the valve and become wedged when the diaphragm is depressed. (http://en.wikipedia.org/wiki/Diaphragm_pump)

Electric diaphragm pumps get used as bilge pumps, but I don’t like them because even small particles lodged in their valves can disable them and, in any case, they have a low flow rate….the total volume of water moved will still be considerably less than that moved by a good-size centrifugal pump operating at just 25% capacity. (Cruising Handbook, p. 220)

Water Pumps

The simplest galley pumps are those integral to the faucet and operated by a lever with vertical or horizontal throw. (Upgrading the Cruising Sailboat, p. 101)

Manual foot-operated galley pumps are preferred by some cooks who want to keep both hands free while pumping. On a moving boat it’s not always easy to brace yourself comfortably to elevate one foot to operate the pump, but foot pumps to free your hands and are neat, out-of-the-way systems that have become quite popular. (Upgrading the Cruising Sailboat, p. 101)

Pumps should be fastened securely, either screwed, or in the case of large or manual pumps, thru-bolted to a bulkhead or other strong surface. (Upgrading the Cruising Sailboat, p. 107)

While hand pumps may save water, I cannot stand the irritation of trying to watch one hand at a time or of washing dishes one-handed….The hands-down….best water deliver system for a boat with limited water capacity is the foot pump….makes the best use of available water….most convenient because it leaves both hands free. (This Old Boat, p. 319)

Foot pumps can be somewhat more difficult to install, not because of the plumbing but because of the mounting….can be screwed directly to the inside face of the cabinet, but the curvature of the hull can make getting to the bottom-mount screw problematic. The solution to this is a longer screw passing through a washer that prevents the screw from disappearing into the mount screw recess. With the head of the screw standing proud, you can see it to fit a screwdriver and the screwdriver can be cocked somewhat to clear the ascending hull. (This Old Boat, p. 320)

Foot pumps are almost always diaphragm pumps. (This Old Boat, p. 321)

Salt water pumps, in my opinion, are totally absurd….the whole ocean is at your door step. All you need is a bucket. In the tropics, algae grow rapidly in salt-water plumbing system and every pump will belch out air that smells like a pig farm. Anyway, it’s more pleasant to wash your dishes on deck… (From a Bare Hull, p. 36)